Turbomachinery, such as turbochargers, have been used as a means of greatly extending the power range and flexibility of internal combustion engines. These devices use engine exhaust to drive a turbine which in turn drives a compressor for supplying a compressed air charge to the engine. In most configurations, the turbine and compressor rotors rotate on a rotor shaft supported on bearings, such as journal, flat disc-type thrust bearings or ball bearings. Although the use of ball bearings improve the turbomachinery operation and efficiency, because of the proximity of the bearings to the hot exhaust gases used to drive the turbine rotor, they are susceptible to damage and are more vulnerable to the problems caused by overheating than journal bearings or flat disc-type thrust bearings.
One design incorporating ball bearings is shown in U.S. Pat. No. 4,179,247, to Osborn. In this design, the bearing assemblies are separated from the turbine and thus are spaced from the intense heat to which the turbine is subjected. The compressor rotor and turbine rotor are located in an overhung position with the compressor rotor positioned between the turbine rotor and the bearings. Further, control structure for controlling the turbine inlet nozzle area is positioned between the turbine side of the turbocharger and the compressor side to insulate the bearings from the turbine exhaust gases.
Because of the criticality of precision ball bearings used in turbomachinery, including turbochargers, bearing life can be extended, and the overall longevity of the turbocharger increased by further reducing heat which may be transferred from the turbine side of the turbomachinery to the bearings. Thus, although the design shown in U.S. Pat. No. 4,179,247 reduces the amount of heat ultimately transferred to the bearings, a need exists for further isolating the bearings to reduce the transfer of heat thereto and for a means for preventing lubricant used for the bearings from reaching elevated temperatures.
Further, it has been demonstrated that providing a separate reservoir of oil for lubrication of the bearings of turbomachinery, rather than use of the oil in the internal combustion engine on which the turbomachinery is mounted, greatly enhances the life of the turbocharger. However, providing such a reservoir as a part of the turbomachinery housing limits the application of prior designs to certain engines because of the restriction on the orientation of the turbocharger for purposes of assuring proper oil delivery to the bearings. Thus, a need exists for a design which permits unlimited orientation of the turbomachinery relative to the engine on which it is mounted.
For proper operation, turbomachinery must function within and maintain very close tolerances between the turbine and compressor rotors and the surrounding housing. This requires that the compressor housing and turbine housing maintain proper concentricity with respect to the compressor and turbine rotors and therefore with respect to each other. Achieving this result is difficult in that such housings are formed of different materials having different coefficients of thermal expansion. Thus, a need exists for a way to maintain concentricity between components.